1. Field of the Invention
The present invention relates to a keypad with which a portable terminal or the like is provided, and more particularly to a keypad with a light guide layer, and a keypad assembly.
2. Description of the Related Art
A keypad used in a conventional portable terminal generally includes a plate-like elastic pad, a plurality of key buttons which are formed on a first side of the elastic pad, and each of which has characters (letters, numerals or symbols) printed on its upper surface, and a plurality of protrusions (or actuators) formed on a second side of the elastic pad, located opposite the first side. Also, it is normal for the portable terminal to have a plurality of light emitting devices (usually 15 to 20 in number) for backlighting the keypad.
FIG. 1 illustrates a sectional view of a keypad assembly of the prior art. The keypad assembly 100 includes a keypad 110, a switch board 150 and a plurality of light emitting diodes (hereinafter referred to as “LED”) 170.
The keypad 110 includes a plate-like elastic pad 120, a plurality of key buttons 140 which are formed on a first side 122 of the elastic pad 120 and each of which has characters (letters, numerals or symbols) printed on its upper surface, and a plurality of protrusions 130 formed on a second side 124 of the elastic pad 120, located opposite the first side 122. Each protrusion 130 on the second side 124 of the elastic pad 120 is arranged in a position corresponding to a center of each key button 140. A plurality of grooves 126 may be formed on the second side 124 of the elastic pad 120. The grooves 126 are disposed around the respective protrusions 130 so as to avoid interferences between the light emitting diodes 170 and the protrusions 130.
The switch board 150 has a plate-like printed circuit board (hereinafter referred to as “PCB”) 155 and a plurality of switches 160 formed on an upper surface, facing the keypad 110, of the PCB 155. Each switch 160 consists of an electrically conductive contact member 162 and an electrically conductive dome 164 completely covering the contact member 162.
The plurality of light emitting diodes 170 are mounted on the upper surface of the PCB 155, and are positioned such that each of them is covered with a corresponding groove 126 of the elastic pad 120.
If a user pushes down any one key button 140, a portion of the keypad 110, located under the key button 140, is deformed onto the switch board 150, and, thus, a corresponding protrusion 130 belonging to the deformed portion of the keypad 110 presses a corresponding dome 164. The pressed dome 164 comes into electrical contact with a corresponding contact member 162.
For operating the switches 160, each light emitting diode 170 may not be located under the corresponding key button 140. Thus, light emitted from each light emitting diode 170 obliquely illuminates the corresponding key button 140 after passing through the elastic pad 120. On this account, there is a problem in that the key button 140 is not uniformly illuminated. In other words, a central portion of each key button 140 is relatively darkly illuminated whereas edge portions of the key button 140 are relatively brightly illuminated. Also, even if a greater number of light emitting diodes are provided so as to uniformly and brightly illuminate the key buttons 140, there occurs a further problem of large power consumption and high manufacturing cost.
To solve these problems, a method is proposed to use inorganic EL (Electro Luminance) for illuminating key buttons. However, the inorganic EL requires an additional inverter for converting DC current to AC current because AC power must be used for the inorganic EL, and electric noise and sound noise occurring in the inorganic EL must be settled beforehand.